Effects of subtle differences in ligand constitution and conformation in metallo-supramolecular self-assembled polygons

3,3'-Bis(pyridin-[n]-ylethynyl)biphenyl (n = 3, 4) and the corresponding 2,2'-bipyridines assemble with (dppp)Pt-II triflate into metallo-supramolecular polygons. Depending on the position of the terminal pyridine N atoms, the assembly reaction leads to different equilibrium products. With the slow ligand exchange on Pt-II complexes, the equilibrium is reached on a many-hour time-scale. During the assembly process, larger polygons form under kinetic control. This was confirmed by time-dependent H-1 and P-31 NMR spectroscopy in line with complementary ESI mass spectrometric experiments. The constitutional difference in the pyridine N-atom position is reflected in the tandem mass spectra of the complex ions. In addition, a highly specific fragmentation process of mass-selected M3L3 ions was observed, which proceeds through a ring contraction yielding smaller M2L2 ions.